To understand the structure of the social networks in which we live is a very interesting problem. As part of the recent surge of interest in networks, there have been active research about social networks[1]}, [2]}, [3]}, [4]}, [5]}, [6]}. Besides some well known common properties such as small-world and community
structure[7]}, [8]}, [9]}, much attention has been dedicated to navigation in real social networks.
